A method for separating a semiconductor wafer into several thousand devices or dies by laser ablation. Semiconductor wafers are initially pre-processed to create multiple devices, such as blue LEDs, on the wafers. The wafers are then mounted with tape coated with a generally high level adhesive. The mounted wafer is then placed on a vacuum chuck (which is itself positioned on a computer controlled positioning table) to hold it in place during the cutting process. The cutting surface is then covered with a protective layer to prevent contamination from the effluent resulting from the actual cutting process. A laser beam is generated and passed through optical elements and masks to create a pattern, such as a line or multiple lines. The patterned laser projection is directed at the wafer at a substantially normal angle and applied to the wafer until at least a partial cut is achieved through it. A mechanical separation process completes the separation when only a partial cut is achieved by the patterned laser projection. The dies are then transferred to a grip ring for further processing.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for separating semiconductor wafers into dies, said method comprising the steps of: directing a patterned laser projection at a surface of a semiconductor wafer, said semiconductor wafer comprising a sapphire substrate and a device layer; applying said patterned laser projection with a given set of parameters until at least a partial cut in said semiconductor wafer is obtained: and separating said semiconductor wafer into dies using said at least partial cut.
2. The method of claim 1 , wherein said device layer comprises a nitride device layer.
3. The method of claim 1 , wherein said sapphire substrate has a bandgap value greater than an energy value for the laser projection.
4. The method of claim 1 , wherein said sapphire substrate has a C-plane orientation.
5. The method of claim 1 , wherein said patterned laser projection is one selected from the group consisting of long lines, multiple lines, multiple parallel lines and grids.
6. The method of claim 1 , further including the step of mechanically breaking a remaining portion of said semiconductor wafer when said at least partial cut is a partial cut.
7. The method of claim 1 , further including the step of mounting said semiconductor wafer on an adhesive tape to maintain dies together after separation.
8. The method of claim 7 , wherein said step of mounting further includes the step of applying a second layer to said adhesive tape when said at least partial cut is a full cut.
9. The method of claimed 8 , wherein said second layer comprises epoxy.
10. The method of claim 1 , wherein said surface is a back/substrate surface of said semiconductor wafer.
11. The method of claim 1 , wherein said surface is a front/epitaxial surface of said semiconductor wafer.
12. The method of claim 1 , wherein a kerf width is <20 m.
13. The method of claim 1 , wherein said at least one partial cut is less than 3.5 mils in depth.
14. The method of claim 1 , wherein said step of directing includes the step of generating laser light emissions capable of cutting the sapphire substrate via laser ablation.
15. The method of claim 1 , wherein said device layer comprises gallium nitride.
16. The method of claim 1 , wherein said device layer comprises gallium arsenide.
17. The method of claim 1 , wherein said device layer comprises aluminum nitride.
18. The method of claim 1 , wherein said device layer comprises indium nitride.
19. The method of claim 1 , wherein said device layer comprises silicon.
20. The method of claim 1 , wherein said device layer comprises III-V material.
21. A method for separating semiconductor wafers into multiple devices, said method comprising the steps of: preparing a semiconductor wafer with a plurality of devices, said semiconductor wafer comprising a sapphire substrate; mounting said semiconductor wafer on a tape; placing a mounted semiconductor wafer on a holding mechanism, said holding mechanism situated on a positioning table; directing a patterned laser projection on to a surface of said mounted semiconductor wafer; applying said patterned laser projection to said mounted semiconductor wafer until at least a partial cut in said mounted semiconductor wafer is obtained; and separating said semiconductor wafer into multiple devices using said at least partial cut.
22. The method of claim 21 , wherein said step of applying further includes the step of positioning said positioning table with respect to said patterned laser projection to permit cutting along different axes and different sections of said mounted semiconductor wafer.
23. The method of claim 21 , wherein said sapphire substrate has a bandgap value greater than an energy value for the laser projection.
24. The method of claim 21 , wherein said patterned laser projection is one selected from the group consisting of long lines, multiple lines, multiple parallel lines and grids.
25. The method of claim 22 , wherein said step of mounting further includes the step of applying a second layer to said tape when said at least partial cut is a full cut.
26. The method of claim 21 , wherein said surface is a back/substrate surface of said semiconductor wafer and a kerf width of a cut is less than 100 m.
27. The method of claim 21 , wherein said surface is a front/epitaxial surface of said semiconductor wafer and kerf width of a cut is less than 100 m.
28. The method of claim 21 , wherein said step of applying uses at least one cut to achieve said at least partial cut, each said at least one cut being less than 3.5 mils in depth.
29. The method of claim 21 , wherein said device layer comprises gallium nitride.
30. The method of claim 21 , wherein said device layer comprises gallium arsenide.
31. The method of claim 21 , wherein said device layer comprises aluminum nitride.
32. The method of claim 21 , wherein said device layer comprises indium nitride.
33. The method of claim 21 , wherein said device layer comprises silicon.
34. The method of claim 21 , wherein said device layer comprises III-V material.
35. A method for making semiconductor devices comprising the steps of: providing a semiconductor wafer, the providing step including the step of, on a sapphire substrate, depositing a device layer; directing a laser through optical elements to form a patterned laser projection; making a plurality of cuts in at least the sapphire substrate via laser ablation using the patterned laser projection; and separating the semiconductor wafer into semiconductor devices using the cuts.
36. The method of claim 35 , wherein said device layer comprises gallium nitride.
37. The method of claim 35 , wherein said device layer comprises gallium arsenide.
38. The method of claim 35 , wherein said device layer comprises aluminum nitride.
39. The method of claim 35 , wherein said device layer comprises indium nitride.
40. The method of claim 35 , wherein said device layer comprises silicon.
41. The method of claim 35 , wherein said device layer comprises III-V material.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
October 23, 1998
July 2, 2002
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